AU2021100103A4 - Method for Determining Staggered Distance of Simultaneous Mining Face of Shallow-Buried Coal Seam Group Based on Pressure-Stabilizing Arrangement - Google Patents
Method for Determining Staggered Distance of Simultaneous Mining Face of Shallow-Buried Coal Seam Group Based on Pressure-Stabilizing Arrangement Download PDFInfo
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- 238000005065 mining Methods 0.000 title claims abstract description 155
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
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- E21C41/00—Methods of underground or surface mining; Layouts therefor
- E21C41/16—Methods of underground mining; Layouts therefor
- E21C41/18—Methods of underground mining; Layouts therefor for brown or hard coal
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- E—FIXED CONSTRUCTIONS
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- E21C—MINING OR QUARRYING
- E21C41/00—Methods of underground or surface mining; Layouts therefor
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Abstract
The invention provides a method for determining staggered distance of a
simultaneous mining face of a shallow-buried coal seam group based on a
pressure-stabilizing arrangement, belonging to the technical field of coal mining,
comprising: finding out the ideal staggered distance range; according to the ideal
staggered distance range, using an ultimate bearing capacity calculation formula during
the plastic slip of rock and soil, to obtain the calculation formula of the maximum depth
Hmax of an upper coal seam floor damage area under the condition of an ultimate abutment
pressure, and further to obtain the calculation formula of the maximum horizontal distance
Lmax of damaged rock strata in an upper coal seam floor; establishing a mechanical model
of pressure-stabilizing and pressure-reducing types in an advancing direction of
simultaneous mining of upper and lower coal seams in double coal seam mining, obtaining
the maximum horizontal distance of damaged rock strata in the upper coal seam floor, the
stress transmission angle of the floor and the spacing between upper and lower coal
seams, and determining the calculation formula of staggered distance in the advancing
direction of pressure-stabilizing and pressure-reducing types; correcting the calculation
result in step 3. The method can effectively reduce the rock pressure strength and surface
damage degree of the working face of the coal seam under simultaneous mining in the
overlapping area of the double coal seams, and realize efficient green mining of the double
coal seam.
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Description
4 /4
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...... ...... . . .. ... ...c... .
. Fi . 7....
i2.2 o ca S4V y X1 B .. ... ..... ....... .... Fig.. . ...... . .
Method for Determining Staggered Distance of Simultaneous Mining Face of
Shallow-Buried Coal Seam Group Based on Pressure-Stabilizing Arrangement
The invention belongs to the technical field of coal mining, in particular to a method
for determining the staggered distance of the simultaneous mining face of the
shallow-buried coal seam group based on the pressure-stabilizing arrangement.
Coal is an important energy source in our country. In order to realize efficient coal
mining, coal enterprises have begun to change from single coal seam mining to double
coal seam mining at the same time. Simultaneous mining of double coal seams mainly
involves two technical problems: One is that the high-intensity mining of double coal
seams causes the overlying strata to move violently, which leads to excessive
concentration of surface tensile stress and serious damage to the surface ecological
environment. The other is that the overlapping area of upper and lower coal seams is
mined at the same time, and the surrounding rock stress of the lower coal seam working
face is complex and severe, which seriously affects the advancing speed and safety of the
lower coal seam working face.
For a long time, the mining technology and research conclusion of single coal seam
have become increasingly mature, while the research on double coal seam mining mainly
involves the location of coal pillar, the influence of concentrated stress, mining methods
and other aspects, and less involves the staggered distance in the advancing direction of
simultaneous mining of upper and lower coal seams. Under the background of
high-efficiency coal mining, green mining and sustainable development, it is of great theoretical significance and practical value to determine the reasonable staggered distance of the advancing direction of the simultaneous mining face of the upper and lower coal seams, and to study the mining technology that takes into account the simultaneous safe and efficient mining of the double coal seam working face and slows down the surface damage.
At present, for the simultaneous mining of upper and lower coal seams in
superimposed areas, the on-site method of stopping mining and avoiding pressure is
mostly adopted to solve the problems of large-area weighting and support crushing of the
working face of lower coal seam, resulting in tight mining continuity and low production
efficiency. At the same time, high-intensity mining has caused serious surface damage and
deteriorated ecological environment. The existing double coal seam mining technology
cannot give consideration to safe and efficient mining and slow down surface damage, and
there is no research on the staggered distance in advancing direction of the upper and
lower simultaneous mining faces of the double coal seam.
Therefore, the present application proposes a method for determining the staggered
distance of the simultaneous mining face of the shallow-buried coal seam group based on
the pressure-stabilizing arrangement.
In order to overcome the shortcomings of the prior art, the invention provides a
method for determining the staggered distance of the simultaneous mining face of the
shallow-buried coal seam group based on the pressure-stabilizing arrangement.
In order to realize the double purposes of safety and high efficiency and slowing
down surface damage in the simultaneous mining process in the superimposed area of
upper and lower coal seams, by using theoretical analysis, UDEC (two-dimensional
plane discrete element method) numerical simulation, the invention analyzes the stress distribution law and surface failure law of surrounding rock of the lower coal seam under different advancing directions and staggered distances of the simultaneous mining faces in the overlapping area of upper and lower coal seams, studies the mutual influence range and influence degree of simultaneous mining working face in the overlapping area of upper and lower coal seams when different advancing directions are staggered, establishes the pressure-stabilizing and pressure-reducing layout models of the same working face in the overlapping area of upper and lower coal seams, determines the calculation formulas of staggered distance in the advancing direction of the two layout modes, corrects and compares the two calculation results according to the practical experience of on-site mining, and obtains a reasonable staggered distance determination method that takes into account both safe and efficient mining and slowing down surface damage. The method can effectively reduce the rock pressure strength and surface damage degree of the working face of the coal seam under simultaneous mining in the overlapping area of the double coal seams, and realize efficient green mining of the double coal seam.
The invention provides the following technical solution:
A method for determining staggered distance of a simultaneous mining face of a
shallow-buried coal seam group based on pressure-stabilizing arrangement, characterized
by comprising steps of:
step 1. using UDEC 2 numerical simulation methods to master stress distribution law
and surface settlement law of surrounding rock of upper and lower simultaneous mining
faces of double coal seams with different staggered distance in an advancing direction of a
working face, analyzing the influence range and degree between the upper and lower
working faces when the working face is simultaneously mined, and obtaining an ideal
dislocation range to provide scientific basis for theoretical analysis and modeling;
step 2. according to the ideal staggered distance range, selecting an ultimate bearing
capacity calculation formula during the plastic slip of rock and soil in elastic-plastic mechanics theory, using the ultimate bearing capacity calculation formula during the plastic slip of rock and soil, to obtain the maximum depth Hmax calculation formula of an upper coal seam floor damage area under the condition of an ultimate abutment pressure, and further to obtain the calculation formula of the maximum horizontal distance Lmax of damaged rock strata in an upper coal seam floor; step 3. according to the result of numerical simulation and mechanical theory analysis, establishing a mechanical model of pressure-stabilizing and pressure-reducing types in an advancing direction of simultaneous mining of upper and lower coal seams in double coal seam mining, synthesizing the maximum horizontal distance of damaged rock strata in the upper coal seam floor obtained through comprehensive consideration of theoretical analysis, the floor stress transmission angle and the distance between the upper and lower coal seams, and determining the calculation formula of staggered distance in the advancing direction of pressure-stabilizing and pressure-reducing types; step 4. correcting the calculation result in step 3 according to the practical mining experience and measured results, to obtain the optimal staggered distance suitable for on-site production in the initial mining stage and the normal mining period of the advancing direction of upper and lower coal seam working faces.
Preferably, in step 1, according to a large number of numerical simulations, when the
staggered distance between the advancing direction of the upper and lower coal seams is
less than 70m, the influence of mining in the upper coal seam begins to spread to the
working face of the lower coal seam, the superposition of mining stress gradually
increases with the decrease of the staggered distance, and the peak value of the
advanced abutment pressure in the working face of the lower coal seam continuously
increases; when the staggered distance arranged side to side is Om, the score of the
advanced abutment pressure in the lower coal seam reaches 11.38MPa, and the
curvature of the surface subsidence curve continuously increases with the decrease of the staggered distance. The analysis shows that pressure-reducing and pressure-stabilizing areas exist in the process of mining lower coal seam, which provides a basis for theoretical analysis and determination of staggered distance formula.
Preferably, step 2 obtains:
M length of yield zone at coal wall position of working face: S= 2KItanQ In
KyH+C.cotq KICmcotqp
ScoW0 e20 °
2co ;T+ °P maximum damage depth of upper coal seam floor: H=ax= 4 22)
maximum horizontal distance of damaged rock strata in upper coal seam floor:
Lmax L+ L2 = H tg?0
wherein horizontal distance between maximum damage depth point of upper coal
seam floor and the working face: L, = Hmtgo0
maximum horizontal distance between the maximum damage depth point of upper
coal seam floor and the goaf compaction critical point:
L, = Stg( + 0 2o 2 2
wherein: ( is the internal friction angle of coal seam, 0; Cm is the cohesion of coal
seam, MPa; M is the mining height of coal seam, m; K is the maximum stress
concentration factor; K, is triaxial stress coefficient; 0 is the internal friction angle of floor
strata, 0; P-average bulk density of overlying strata; H-buried depth of coal seam.
Preferably, the step 3 comprises steps of:
step 3.1. according to the results of theoretical analysis, establishing a mechanical
model of pressure-stabilizing and pressure-reducing types for mining the upper and lower working faces of the double coal seams, and determining the quantitative influence parameters; step 3.2. synthesizing the mechanical model in the step 31 and the numerical calculation results of UDEC 2 o, to establish the pressure-stabilizing and pressure-reducing type staggered distance formulas; pressure-stabilizing staggered distance calculation formula: Wmin=X+B+hcota where: h is the average distance between upper and lower coal seams, the unit is m; a is the stress influence angle, the unit is0; B is the maximum roof control distance of the upper coal seam, the unit is m; X, is the horizontal distance between the critical point Y of the compaction area of the goaf of the upper coal seam and the hydraulic support, the unit is m; X, is obtained from the maximum horizontal distance Lmax of the damaged rock strata in the upper coal seam floor; pressure-reducing staggered distance formula: Jmax=Wmin-Lo
Jmin=B+X2+hcot a+S2
where: Wmin is the minimum value of the pressure-stabilizing staggered distance, the
unit is m; Lois the average periodic caving step distance of the upper coal seam, and the
unit is m; Jmax is the maximum staggered distance of the pressure-reducing arrangement,
and the unit is m;
Jmin is the minimum staggered distance of the pressure-reducing arrangement, and
the unit is m; h is the average distance between upper and lower coal seams, the unit is m;
a is the stress influence angle, the unit is°; B is the maximum roof control distance of the
upper coal seam, the unit is m; X2 is the horizontal distance between the critical point of
the roof failure zone of the lower coal seam and the support of the upper coal face, the unit
is m.
Preferably, in the step 4, the pressure-stabilizing calculation formula is modified in combination with the on-site mining experience to obtain the optimal staggered distance calculation formula suitable for the on-site initial mining stage and the normal mining stage, so as to guide the on-site mining practice; correction formula for initial mining stage: Wc=Wmin+1.4Lc correction formula for normal mining stage: Wz=Wmin+2Lz in the formula, Lc is the basic top initial collapse step distance, the unit is m; Lz is the basic top periodic collapse step distance, the unit is m.
The method for determining staggered distance of the advancing direction of upper
and lower simultaneous mining faces of the double coal seams provided by the invention
has the following beneficial effects:
1. The working face of the lower coal seam is arranged in a pressure-stablizing type
to realize safe mining. High intensity mining of double coal seams and the law of
overburden caving and mine pressure in the working face of lower coal seam are different
from those of single-layer coal mining. In the double coal seam mining in the stacked area,
the stress state of surrounding rock in the working face of the lower coal seam is more
complex and changeable, and the ground pressure is violent, which seriously threatens
the safety of working face personnel and the utilization rate of equipment. According to the
invention, the staggered distance in the advancing direction of the working face
determined by the invention avoids the stress superposition area of surrounding rock
simultaneously mined by the upper and lower coal seams and ensures the safety of mining
personnel and equipment of the lower coal seam.
2. The uniform settlement of overburden is realized, the generation of
concentrated tensile stress on the surface is avoided, and green mining is realized. The
overburden caving is severe during mining in the overlapping area of double coal seams.
Due to the support effect of coal wall, the uneven settlement of overlying strata is obvious,
and the internal stress distribution of overlying strata is greatly differentiated, which leads to obvious concentrated tensile stress areas and obvious tensile cracks on the surface.
Based on this, the combination of numerical simulation and physical simulation is used to
study the overburden caving law and surface subsidence law with different staggered
distance in the advancing direction of the upper and lower simultaneous mining faces in
the superimposed area, and the staggered distance to reduce the degree of surface
damage is determined.
3. The invention solves the problem of continuous tension on site and realizes
efficient mining in coal mining enterprises. The upper and lower coal seams are mined at
the same time in the overlapping area, and the advancing speed of the lower coal seam
working face is affected by the upper coal seam mining, resulting in tight mine connection
and low production efficiency. By determining the safe staggered distance in the advancing
direction, the mining basis is provided for on-site production, the difficult problem of
continuous tension is reasonably avoided, and the purpose of high yield and high
efficiency production is achieved.
4. Based on the numerical simulation calculation, theoretical analysis and
practical experience of on-site mining, the reasonable staggered distance method of
advancing direction of upper and lower simultaneous mining faces of shallow-buried
double coal seams is determined, the calculation model is established, and the
quantifiable parameters and quantitative calculation formulas in the model are given,
which can effectively guide on-site mining and realize efficient mining of shallow-buried
double coal seams.
Fig. 1 is a stress diagram of surrounding rock of a coal seam working face under
different staggered distances in an advancing direction;
Fig. 2 is a graph showing the peak value of advanced abutment pressure at a working
face of lower coal seam;
Fig. 3 is a surface subsidence curve under different staggered distances in an
advancing direction;
Fig. 4 is a distribution law of front and rear abutment pressure of the working face;
Fig. 5 is a pressure-stabilizing mechanical model;
Fig. 6 is a pressure-reducing mechanical model;
Fig. 7 is a pressure-stabilizing calculation model;
Fig. 8 is a pressure-reducing calculation model.
To enable those skilled in the art understand the technical solution of the invention
better, the invention will be further described in detail with the appended drawing and
specific embodiments. The following embodiments are only for more clearly illustrating the
technical solution of the invention, other than limiting the scope of protection of the
invention.
The invention provides a method for determining the staggered distance of the
simultaneous mining face of the shallow-buried coal seam group based on the
pressure-stabilizing arrangement, which comprises the following steps:
Step 1: Stress Distribution Law of Different Staggered Distances in
Advancing Direction of Upper and Lower Simultaneous Mining Face in Double Coal
Seams
According to the mining situation of the upper and lower simultaneous mining faces
of shallow buried double coal seams, the UDEC numerical simulation calculation is
adopted to obtain the stress distribution law of different staggered distances in the
advancing direction of the upper and lower simultaneous mining faces, as shown in Fig. 1.
(1) Stress Distribution Law of Surrounding Rock in Lower Coal Seam Working
Face.
The surrounding rock stress of coal seam working face in the staggered distance in
different advancing directions is shown in Fig. 1. The influence of the upper coal seam
mining on the floor strata is distributed in an erected "splayed" shape. The surrounding
rock stress of the lower coal seam working face is affected by the dual effects of the coal
seam mining and the upper caving overburden. With the reduction of the staggered
distance between the advancing directions of the lower coal seam working face and the
upper coal seam working face, the influence of the lower coal seam working face on the
mining of the upper coal seam working face is more and more obvious. Considering the
influence of the thickness of interval strata, the change can be expressed by the ratio of
the staggered distance I1] in the advancing direction of the working face toand the eeal
seam-spacing (f[2] between two coal seams (i.e., the ratio of the staggered distance in
the advancing direction kz).
When the staggered distance in the advancing direction is 100 m, namely, about 3h,
the caving strata behind the goaf of the upper coal seam have been compacted, and the
working face of the lower coal seam is similar to that of single-layer coal mining, which is
basically not affected by the mining stress of the upper coal seam.
When the staggered distance in the advancing direction is 60-70 m, namely, 2h, the
influence of mining in the upper coal seam starts to spread to the working face in the lower
coal seam, and the stress superposition gradually increases.
When the staggered distance in the advancing direction is less than 30 m, namely, 1h,
the surrounding rock stress increase area of the lower coal seam working face and the
surrounding rock stress increase area of the floor of the upper coal seam working face are
completely connected and superimposed, resulting in serious wall fragmentation of the
lower coal seam working face and sharp rise of support pressure.
(2) Peak law of advanced abutment pressure in working face of lower coal seam.
According to the calculation results, when the staggered distance in the advancing
direction is 100, 70, 35 and 0 m, the peak value of advanced abutment pressure in the
elastic area in front of the coal wall of the lower coal seam working face is 5.30, 6.00, 9.23
and 11.38 MPa respectively. With the decrease of the staggered distance in the advancing
direction of the working face, the peak value of the advanced abutment pressure of the
working face of the lower coal seam increases continuously, as shown in Fig. 2. It can be
seen that the staggered distance in the advancing direction between the lower coal seam
working face and the upper coal seam working face should be more than 2 times the coal
seam spacing, namely, 2h=70 m.
Step 2: Surface Settlement Law of Different Staggered Distances in
Advancing Direction of Upper and Lower Simultaneous Mining Faces in Double
Coal Seams
The surface subsidence curve of the staggered distance in different advancing
directions is shown in Fig. 3. The maximum subsidence value when the surface is fully
mined is basically the same, about 5.1 m. However, the curvature of surface subsidence
varies greatly in the staggered distance in different advancing directions, indicating that the
degree of surface tensile failure is obviously different. The surface subsidence curvature is
very large and the subsidence gradient is more than 4 cm/m when the staggered distance
in the advancing direction is less than 1h (h=35 m); The surface subsidence curvature
obviously decreases to 3.7 cm/m when the staggered distance in the advancing direction
is 2h; When the staggered distance in the advancing direction is more than 3h, the
curvature of the surface subsidence is very small and the damage to the surface is small.
Step 3: Theoretical Analysis of Different Staggered Distances in Advancing
Direction of Upper and Lower Simultaneous Mining Faces in Double Coal Seams
(1) Distribution Law of Supporting Pressure in Working Face
The stress in the stope is redistributed due to coal seam mining, and the formed
abutment pressure can be generally divided into decompression area, pressurization area
and pressure stabilization area. The range from the peak position of the abutment
pressure in front of the working face to the coal wall is the limit equilibrium area, and the
elastic area is in the coal body, as shown in Fig. 4, where a-pressure increasing area;
b-pressure reducing zone; c-pressure stabilizing area; 7 -average bulk density of
overlying strata; H-buried depth of coal seam; K is the maximum stress concentration
factor.
(2) Failure Law of Coal Seam Mining Floor
According to the theory of elastoplastic mechanics, the floor strata can be divided
into three areas under the influence of abutment pressure, namely, active stress limit area,
transitional stress limit area and passive stress limit area. According to the formula for
calculating the ultimate bearing capacity of rock and soil's plastic sliding proposed by
A.S.Vesic, the formula for calculating the maximum depth and length of the failure area of
the upper coal seam floor under the condition of ultimate abutment pressure is obtained
after correction.
1) For the determination of the maximum damage depth of coal seam floor , the length S of coal seam yield area is:
M KyH + C.cotp S= 2KItanq In KiCmCotp (1)
wherein: ( is the internal friction angle of coal seam, 0; Cm is the cohesion of coal
seam, MPa; M is the mining height of coal seam, m; K is the maximum stress
concentration factor; K, is triaxial stress coefficient; 7-average bulk density of overlying
strata; H-buried depth of coal seam. The maximum damage depth of coal seam floor Ha
is:
Scosq0 S ?* e 4 + O Hmax= 242)2cos; (2)
where: ( 0 is the internal friction angle of floor strata, °.
2) The maximum horizontal distance Lmaxof the damaged rock strata in the upper
coal seam floor of the coal seam is calculated, and the horizontal distance LI from the
maximum damaged depth point of the floor to the working face is:
L, = HmatgRo (3)
The maximum horizontal distance L 2 between the maximum damage depth point of
floor and the goaf compaction critical point is:
L2 = Stg( + 0 e2 2 2 (4)
Then
Lmax = L+ L 2 = Htg 0 (5)
Step 4. Pressure-stabilizing and pressure-reducing type mechanical model of
the upper and lower simultaneous mining face of the double coal seams
The numerical results of UDEC 2 D provide the basis for selecting the appropriate
mechanical theory. According to the analysis of UDEC 2 D numerical calculation results, the
calculation formula of ultimate bearing capacity in rock and soil's plastic slip in
elastoplastic mechanics theory is more suitable. According to the calculation formula of
ultimate bearing capacity in rock and soil's plastic slip, the failure law of upper coal seam
floor is obtained. Based on the spatial superposition relationship between upper and lower
coal seams in the practice of double coal seam mining, combined with the failure law of
upper coal seam floor, the mechanical models of pressure-stabilizing and
pressure-reducing types in the advancing direction of upper and lower simultaneous
mining face of the double coal seams are established.
(1) Pressure-stabilizing mechanical model
According to the theory of pressure stabilizing area arrangement, the working face of
the lower coal seam must be ensured to be located in the re-compaction stable area of the
goaf of the upper coal seam, and the mining of the lower coal seam must be carried out
after the overlying strata of the working face of the upper coal seam cave and stabilize.
The mechanical model is shown in Fig. 5. Point Y in the figure is the critical point for
compaction of the goaf of the upper coal seam. The roof of the goaf on the left side of point
Y is collapsed and compacted. The horizontal staggered distance between the working
face of the lower coal seam and the working face of the upper coal seam shall be greater
than the length of Section AY, which can be obtained from the maximum horizontal
distance Lmaxof the damaged rock strata in the upper coal seam floor, wherein Si is the
length of the coal seam yield area of the upper coal seam working face; a is the stress
influence angle; r is the radius of influence.
(2) Pressure-reducing mechanical model
The layout of pressure reducing area must ensure that the working face of the lower
coal seam is located in the caving arch structure of the overlying strata of the upper coal
seam, i.e., the position where the roof support pressure is relatively small. The mechanical
model of the pressure reducing area is shown in Fig. 6. Point C in the figure is the deepest
point of failure of the upper coal seam floor, and the corresponding point P is the critical
point of failure of the lower coal seam roof. The lower coal seam working face must be
arranged on the left side of point P. The length of Section AP can be obtained from the
horizontal distance L, between the maximum failure depth point of the floor and the
working face. S2 is the length of the coal seam yield area of the lower coal seam working
face.
Step 5: Calculation formula of reasonable staggered distance in advancing
direction of upper and lower simultaneous mining face of double coal seams
(1) The pressure-stabilizing calculation model is shown in Fig. 7. XI is the length of
Section AY, which can be obtained from the maximum horizontal distance Lmax of the
damaged rock strata in the upper coal seam floor. Therefore, the minimum value Wmin of
reasonable staggered distance in the advancing direction of the simultaneous mining face
is:
Wmin=X,+B+hcota (6)
Where: h is the average distance between upper and lower coal seams, m; a is the
stress influence angle, 0; B is the maximum roof control distance of the upper coal seam,
m; X, is the horizontal distance between the critical point Y of the compaction area of the
goaf of the upper coal seam and the hydraulic support, m;
(2) The pressure-reducing calculation model is shown in Fig. 8. According to the
pressure-reducing arrangement theory, the working face of the lower coal seam is
arranged in the arch structure of the roof of the upper coal seam, and the average periodic
caving step distance Lo of the upper coal seam is subtracted from the minimum value of
the staggered distance of the pressure-stabilizing arrangement, and the maximum value
Jmax of the staggered distance in the advancing direction is:
Jmax=Wmin-Lo (7)
where: Wmin is the minimum value of staggered distance in pressure-stabilizing
arrangement, m; Lo is the average periodic caving of the upper coal seam, m.
The minimum value of staggered distance of pressure-reducing type must meet the
requirement that the working face of the lower coal seam is not affected by the dynamic
pressure of the upper coal seam. X2 is the length of Section AP, which can be obtained
from the horizontal distance L, between the maximum failure depth point of the floor and
the working face. Therefore, the calculation formula of the staggered distance Jmin in the
advancing direction is:
Jmin=B+X2+hcot a+S2 (8)
Where: h is the average distance between upper and lower coal seams, m; a is the
stress influence angle, 0; B is the maximum roof control distance of the upper coal seam,
m; X2 is the horizontal distance between the critical point P of the roof failure area of the
lower coal seam and the support of the upper coal working face, m.
In mining practice, it is difficult to control the pressure reducing area due to its small
scope. The staggered distance obtained through the principle of pressure stabilizing area
can prevent the lower coal seam from being affected by the superimposed stress of the
upper coal seam and is easy to be applied in the field. Therefore, the pressure-stabilizing
calculation formula should be adopted for the calculation of reasonable staggered distance
in the advancing direction of the upper and lower simultaneous mining face in
shallow-buried double coal seams.
6. Correction of Calculation Formula for Reasonable Staggered Distance in
the Advancing Direction
(1) Initial mining stage. According to the field measurement, the initial caving step
distance of overlying strata in the working face is relatively large, and the duration is
generally 2-3 d. In the initial mining stage, the influence of the first caving step distance of
the upper coal seam shall be considered, and the correction formula is W=Wmin +1.4Lc,
where Lc is the first caving step distance of the basic roof, m.
(2) During normal mining. In the normal mining process of upper coal seam,
considering the influence of periodic caving strata pressure, the correction formula is Wz=
Wmn+ 2Lz, where Lz is the basic roof periodic caving step distance, m.
Embodiment 1
Taking a coal mine in northern Shaanxi as an example, the method for determining
staggered distance in the advancing direction of upper and lower simultaneous mining
faces of the double coal seams is further illustrated through specific embodiments.
According to the mining conditions of typical shallow coal seams in northern Shaanxi,
the application of the method is illustrated by taking the mining of upper and lower
simultaneous mining face of double coal seams in the eastern part of the northern wing of
a mine as an example. The mining area adopts inclined shaft development, one-time
mining full-height long-arm comprehensive mechanized coal mining method and all caving
method to manage the roof. The inclination angle of the coal seam is about 10, which is a
nearly horizontal coal seam. At present, coal seam 1-2 and coal seam 2-2 are mainly mined.
The internal friction angles of coal seam 1-2 and coal seam 2-2 are 37.50 and 38.50
respectively. The cohesive forces are 1.3 MPa and 1.4 MPa. The average mining heights
of coal seam 1-2 and coal seam 2-2 are 1.89 m and 5.00 m respectively. The average stress
concentration coefficient of coal seam 2-2 is 5.0, the average bulk density of overlying
strata is 23 kN/m3 , the average buried depths of coal seam 1-2 and coal seam 2-2 are 110
m and 145 m respectively. The internal friction angle of coal seam 1-2 floor strata is 42, the
caving angle of strata is 490, the average interval between coal seam 1-2 and coal seam 2-2
is 35 m, the average periodic caving step distance of coal seam 1-2 is 11.8 m, and the
maximum roof control distance of coal seam 1-2 is 6 m.
At present, the mining of coal seam 1-2 and the mining of coal seam 2-2 have great
influence on each other. When coal seam 2-2 is mined, in order to avoid the influence of
concentrated stress in coal seam 1-2, it is necessary to limit the speed of mining speed,
keep a certain staggered distance from the working face of coal seam 1-2, and stop mining
to avoid pressure. On-site determination of the range of staggered distance according to
mining experience lacks scientific basis, resulting in continuous tight mine production.
According to the occurrence conditions of the coal seam in the mining area, the
method for determining the staggered distance in the advancing direction of the upper and
lower simultaneous mining face of the double coal seams provided by the invention is
adopted, and a pressure-stabilizing calculation method is proposed to determine the staggered distance in the advancing direction of the upper and lower simultaneous mining face of the shallow-buried double coal seams. By substituting the above parameters into formulas (6), (7) and (8), we can get Wmin = 81 m, Jmax = 69.2 m, Jmin = 56 m. In mining practice, it is difficult to control the pressure reducing area due to its small scope. The staggered distance obtained through the principle of pressure stabilizing area can prevent the lower coal seam from being affected by the superimposed stress of the upper coal seam. Therefore, the staggered distance in the advancing direction of the simultaneous mining face in the eastern part of the northern wing is determined according to the pressure-stabilizing type, i.e. the staggered distance is more than 81 m.
Correction of the staggered distance in the advancing direction of upper and lower
simultaneous mining face in shallow-buried double coal seams.
1) Initial mining stage. According to the field measurement, the initial caving step
distance of overlying strata in the working face is relatively large, and the duration is
generally 2-3 d. In the initial mining stage, the influence of the initial caving step distance of
the upper coal seam should be considered. The empirical formula is W=Wmin +1.4Lc, and
the first caving step distance of 1-2 coal seam is Lc=29.7 m. It can be concluded that the
staggered distance in the advancing direction between 2-2 coal seam and 1-2 coal seam in
the initial mining stage should be greater than 123 m.
2) During normal mining. In the normal mining process of upper coal seam,
considering the influence of periodic caving, the empirical formula of the staggered
distance of the simultaneous mining face is Wz=Wmin+2Lz, and the periodic caving step
distance is 1-2 coal seam Lz=11.8m, which can be substituted into the formula to obtain
that the staggered distance in the advancing direction of the simultaneous mining face of
2-2 coal seam and 1-2 coal seam shall be greater than 105 m during normal mining.
Therefore, the reasonable staggered distance in the advancing direction between the
2-2 coal seam working face and the 1-2 coal seam working face is as follows: The staggered distance in the initial mining stage is more than 123m, and the staggered distance in the normal mining stage is more than 105m.
After the above mining method is adopted, the coal wall of the working face of coal
seam 2-2 is located in the pressure stabilizing area behind the goaf of coal seam 1-2,
avoiding the influence of concentrated stress of the working face of coal seam 1-2 . The
staggered distance determined by the method is easy to realize in on-site mining, the mine
connection is easy, and the efficient mining of shallow-buried double coal seams is
realized.
The above-described embodiments are only preferred embodiments of the invention,
and the scope of protection of the invention is not limited thereto. Any simple change or
equivalent replacement of the technical solution that can be readily obtained by those
skilled in the art within the scope of the disclosed technology of the invention falls into the
protection scope of the invention.
Claims (5)
1. A method for determining staggered distance of a simultaneous mining face of a
shallow-buried coal seam group based on pressure-stabilizing arrangement, characterized
by comprising steps of:
step 1. using UDEC 2 numerical simulation methods to master stress distribution law
and surface settlement law of surrounding rock of upper and lower simultaneous mining
faces of double coal seams with different staggered distance in an advancing direction of a
working face, analyzing the influence range and degree between the upper and lower
working faces when the working face is simultaneously mined, and obtaining an ideal
dislocation range;
step 2. according to the ideal staggered distance range, using an ultimate bearing
capacity calculation formula during the plastic slip of rock and soil, to obtain the maximum
depth Hmax calculation formula of an upper coal seam floor damage area under the
condition of an ultimate abutment pressure, and further to obtain the calculation formula of
the maximum horizontal distance Lmaxof damaged rock strata in an upper coal seam floor;
step 3. establishing a mechanical model of pressure-stabilizing and pressure-reducing
types in an advancing direction of simultaneous mining of upper and lower coal seams in
double coal seam mining, synthesizing the maximum horizontal distance Lmax of damaged
rock strata in the upper coal seam floor, the floor stress transmission angle and the
distance between the upper and lower coal seams, and determining the calculation
formula of staggered distance in the advancing direction of pressure-stabilizing and
pressure-reducing types;
step 4. correcting the staggered distance calculation formula in step 3 to obtain the
optimal staggered distance suitable for on-site production in the initial mining stage and
the normal mining period of the advancing direction of upper and lower coal seam working
faces.
2. The method for determining staggered distance of the advancing direction of upper
and lower simultaneous mining faces of the double coal seams according to claim 1,
characterized in that in step 1, according to a large number of numerical simulations, when
the staggered distance between the advancing direction of the upper and lower coal
seams is less than 70m, the influence of mining in the upper coal seam begins to spread to
the working face of the lower coal seam, the superposition of mining stress gradually
increases with the decrease of the staggered distance, and the peak value of the
advanced abutment pressure in the working face of the lower coal seam continuously
increases; when the staggered distance arranged side to side is Om, the score of the
advanced abutment pressure in the lower coal seam reaches 11.38MPa, and the
curvature of the surface subsidence curve continuously increases with the decrease of the
staggered distance.
3. The method for determining staggered distance of the advancing direction of upper
and lower simultaneous mining faces of the double coal seams according to claim 1,
characterized in that the step 2 obtains:
M KyH+C.cotQ length of yield zone at coal wall position of working face: S= 2K tangIn KCmcot
. 2c (o" + 1 w
maximum damage depth of upper coal seam floor: =2co 4 2O)
maximum horizontal distance of damaged rock strata in upper coal seam floor:
La = Ll + L2 = H..tgqo
wherein horizontal distance between maximum damage depth point of upper coal
seam floor and the working face: L1 = HatgeO
maximum horizontal distance between the maximum damage depth point of upper
coal seam floor and the goaf compaction critical point:
L, =Stg(- + -0
) 2 2
wherein ( is the internal friction angle of coal seam, and the unit is 0; Cm is the
cohesion of coal seam, and the unit is MPa; M is the mining height of coal seam, and the
unit is m; K is the maximum stress concentration factor; K, is triaxial stress coefficient; O
is the internal friction angle of floor strata, the unit is 0; 7 -average bulk density of overlying
strata; H-buried depth of coal seam.
4. The method for determining staggered distance of the advancing direction of upper
and lower simultaneous mining faces of the double coal seams according to claim 3,
characterized in that the step 3 comprises steps of:
step 3.1. according to the results of theoretical analysis, establishing a mechanical
model of pressure-stabilizing and pressure-reducing types for mining the upper and lower
working faces of the double coal seams, and determining the quantitative influence
parameters;
step 3.2. synthesizing the mechanical model in the step 31 and the numerical
calculation results of UDEC 2o, to establish the pressure-stabilizing and pressure-reducing
type staggered distance formulas;
pressure-stabilizing staggered distance calculation formula: Wmin=XI+B+hcota
where: h is the average distance between upper and lower coal seams, the unit is m; a is the stress influence angle, the unit is 0; B is the maximum roof control distance of the
upper coal seam, the unit is m; X, is the horizontal distance between the critical point Y of
the compaction area of the goaf of the upper coal seam and the hydraulic support, the unit
is m; X, is obtained from the maximum horizontal distance Lmax of the damaged rock strata
in the upper coal seam floor;
pressure-reducing staggered distance formula: Jmax=Wmin-Lo
Jmin=B+X2+hcot a+S2 where: Wmin is the minimum value of the pressure-stabilizing staggered distance, the unit is m; Lois the average periodic caving step distance of the upper coal seam, and the unit is m; Jmax is the maximum staggered distance of the pressure-reducing arrangement, and the unit is m;
Jmin is the minimum staggered distance of the pressure-reducing arrangement, and
the unit is m; h is the average distance between upper and lower coal seams, the unit is m;
a is the stress influence angle, the unit is°; B is the maximum roof control distance of the
upper coal seam, the unit is m; X2 is the horizontal distance between the critical point of
the roof failure zone of the lower coal seam and the support of the upper coal face, the unit
is m.
5. The method for determining staggered distance of the advancing direction of upper
and lower simultaneous mining faces of the double coal seams according to claim 4,
characterized in that in the step 4, the pressure-stabilizing calculation formula is modified
in combination with the on-site mining experience to obtain the optimal staggered distance
calculation formula suitable for the on-site initial mining stage and the normal mining stage,
so as to guide the on-site mining practice;
correction formula for initial mining stage: Wc=Wmin+1.4Lc
correction formula for normal mining stage: Wz=Wmin+2Lz
in the formula, Lc is the basic top initial collapse step distance, the unit is m; Lz is the
basic top periodic collapse step distance, the unit is m.
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